Hearing aid



June 29, 1948. 5, LYBARGER 2,444,302

HEARING AID Fild March 16, 1945 5 Sheets -Sheet 1 INVENTOR.

Jime 29, 1948. s. F. LYBARGER HEARING AID 5 Sheets-Sheet 2 Filed March 16, 1945 June 29, 1948. S F LYBARGER 2,444,302

HEARING AID Filed March 16, 1945 3 Sheets-Sheet 3 Patented June 29, 1948 HEARING AID Samuel F. Lybarger, Pittsburgh, Pa., assignor to E. A. Myers & Sons, Mount Lebanon, Pittsburgh, Pa., a partnership consisting of Edward A. Myers, Edwin J. Myers, and Samuel F. Ly-

barger Application March 16, 1943, Serial No. 479,383

11 Claims.

This invention relates to wearable hearing aids for the hard of hearing.

The average hearing aid receives a great deal of hard usage by the wearer. It is subjected to dropping and other mechanical shocks which may damage the amplifier tubes or other parts of the instrument. The average hearing aid also is exposed to perspiration and humidity as well as the entrance of dust and powder and other undesirable matter. In addition, every hearing aid occasionally requires new vacuum tubes to replace old ones that have become worn out. Most modern hearing aids use a crystal type microphone which is extremely sensitive, but which may be seriously damaged if heated to a temperature higher than 120 F.

All of this shows that one of the most important factors affecting the sale and use of a hearing aid is its adaptability to quick and ready servicing at the point of sale. In many cases this servicing must be done by persons who are not technicians and, therefore, the servicing must be as simple as possible. In fact, if the instrument is not readily serviceable, many dealers will make no attempt at it but will send the hearing aid back to the factory. This has several drawbacks. It deprives the user of his own hearing aid for a relatively long period of time, it requires the manufacturer to spend time repairing instruments, and it requires the dealer to keep on hand a non-income producing stock of hearing aids for the purpose of lending'them to customers whose instruments are being repaired.

Sometimes a magnetic receiver is more suitab-le, and in other cases a crystal receiver may be preferred, for they have difierent frequency response characteristics and the magnetic receiver may be more rugged under certain conditions. With prior hearing aids, magnetic and crystal receivers have required different amplifier units,

thus making it necessary for manufacturers to make two types of amplifiers, and for dealers to carry a stock of both types.

It is among the objects of this invention to provide a hearing aid which is easy to manufacture; which can be easily serviced; which includes an amplifier unit that can be used interchangeably with both crystal and magnetic receivers; which has a thin case for the microphone and amplifier; in which all of the condensers and resistors of the amplifying circuit and their connecting wiring are hidden from view and protected when the case is opened; in which the amplifier tubes are protected from shock; and

in which a combined switch and volume control of simple and durable construction is used.

In accordance with this invention, a microphone and amplifier unit are mounted in the same case which is divided into front and back sections detachably connected together. The microphone is permanently fastened to the front section and is automatically connected to and disconnected from the amplifier when the case is closed and opened, respectively. The elements of the amplifying circuit are all mounted on a supporting plate that is detachably connected to the back section of the case. Practically everything except the amplifier tubes is mounted on the back of the plate within the back of the case. The tubes are resiliently supported by their terminal wires and can be replaced without exposing the rest of the amplifier elements to View or to tampering. The amplifier unit includes a combined switch and volume control of rugged and compact design. The amplifier circuit is such that either a magnetic or a crystal receiver can be used with it by merely using a different battery plug which contains the particular output coupling element necessary for the type of receiver used in each instance.

The preferred embodiment of the invention is illustrated in the accompanying drawings in which Fig. l is a view of my hearing aid using a crystal receiver; Fig. 2 is a similar view of my hearing aid using a magnetic receiver; Fig. 3 is an enlarged view showing the battery plug for the magnetic receiver opened and its two parts placed beside each other with the top part bottom side up; Fig. 4 is a typical circuit diagram including a crystal receiver; Fig. 5 is a typical diagram of the plug and cord circuit by which a magnetic receiver can be connected to the amplifier circuit; Fig. 6 is a side view of the microphone case partly broken away; Fig. '7 is a view of the front of the amplifier unit mounted in the back section of the case; Fig. 8 is a rear view of the amplifier unit; Fig. 9 is an enlarged top view of the amplifier unit; Fig. 10 is an exploded view showing the case in vertical section and the amplifier unit in elevation; Fig. 11 is an inside view of the front section of the case; and Figs. 12 and 13 are enlarged views of an amplifier tube as seen from front and side, respectively.

Referring to Fig. 1 of the drawings, a hearing aid case I contains a microphone and an amplifier unit to be described later which are connected by an electric plug 2 and wire cord 3 to a battery plug 4 plugged into the socket of a B battery 5. The B battery is detachably connected-by a pair of wires to an A battery 1. The battery plug contains a choke 8 that is connected in the battery circuit. Also connected to the case by means of a plug 9 is an electric cord If which is attached to a crystal receiver l l adapted to be worn in the ear by a hard of hearing person.

Case i and the elements therein are also adapted to be used with a magnetic receiver instead of a crystal receiver. Such a substitution is illustrated in Fig. 2 wherein a single plug I3 is plugged into the bottom of the case. This plug is connected by an electric cord I4 to a battery plug 15 attached to the B battery 5. As shown in Fig. 3, the cord is composed of five wires that enter the plug shell l6 through a notch i? in its lower end. The upper surface of the plug base supports a bias resistor it connected to two of the pins of the plug, and four fiat terminal members l9 extending inwardly from the corners of the base. The outer ends of these terminals are perforated to receive the screws by which the base is attached to the shell. From two of the terminals, wires 2c extend out to a magnetic receiver '2! '(Fig. 2). The shell contains an output coupling element in the form of a transformer 23 the primary and secondary leads of which terminate in perforated terminal members '24.. These members are positioned at the corners of the shell so that when the base is applied to it terminals I9 will engage terminals 24 and thereby connect the transformer in the circuit.

Battery plugs 4 and 15 are made substantially alike, except that one contains a choke and the other a transformer, and the bias resistors in the plugs may be of different values.

The circuit that makes it possible to use either type of receiver with my amplifier unit is illustrated diagrammatically in Fig. 4. As no claim is made herein to this circuit per se, its elements will merely be enumerated. Thus, as shown in Fig. 4, case I contains a microphone 26, a tone control switch 21, tone control resistor 28, tone control condenser 29, a pentode tube 30, a screen by-pass condenser 31 and a screen dropping resistor 32 for the tube, a plate coupling resistor 33, a decoupling condenser 34, a decoupling resistor 35, a coupling condenser 36, a volume control 31,, a second amplifying tube 38, a screen dropping resistor 33 and a screen 'by-pass condenser 40 for the second tube, a plate resistor 4 a coupling condenser 42, a grid resistor '43, output tube 44, an output coupling condenser a crystal receiver shunting resistor 46, an optional by-pass condenser 41, a filament switch 48, and seven electric sockets ,49. The crystal receiver plug '9 is adapted to be plugged into the two sockets connected to the shunting resistor 4'6, while the other five sockets are adapted to receive the .plug '2 connected to the battery plug 4 which contains the choke 8 and a bias resistor 50. In case it is desired to use magnetic receiver 21 in place of crystal receiver ll, plug I3 is plugged into the'five sockets 49 at the righthand end of the row, as shown in Fig. '5. By polarizing certain sockets, proper location of the plug is assured. This plug is connected to battery plug IS the construction of which has been described above in connection with Fig. 3.

As shown in Figs. 6, 7, 10, and 11, the microphone case 'I is divided near its center into front an'd'ba'ck'sectionsii and 52 detachably connected together by screws or the like. The microphone 26 is located in'the upper vpart of the case to the front wall of which it is permanently connected by a flexible gasket 53 cemented to both the microphone and case. The two wires from the microphone are connected to a pair of electric sockets 54 projecting rearwardly from an insulating block 55 rigidly mounted on a shelf 56 integral with the front section of the case. These sockets frictionally receive contact pins 51 projecting forward from an insulating plate 58 that divides the interior of the case into front and rear compartments. This thin plate may be made from phenolic material. The edges of this plate fit into a groove around the inside of the case formed by providing the meeting edges of the two sections with cooperating recesses 59. The plate fits snugly in the front of the back section to which it is detachably secured by screws 60. If desired, the rear compartment thus formed in the case can be sealed by a narrow sealing gasket clamped between the edge of the .plate and the case. This plate forms the base of the amplifier unit and supports everything in the case except the microphone unit.

Mounted on the front of plate 58 in the cavity below the microphone are the three vacuum tubes 30, 38, and 44 by which sound picked up by the microphone is amplified. Each of these tubes is supported by its wire terminals 62 that project from one end into electric sockets or binding posts 63 mounted on the plate. To strengthen the ends of the terminals and to prevent them from being chewed up by the binding post screws, they are reinforced, such as by being doubled back on themselves and soldered, as shown in Fig. 12. To prevent severe shocks and vibrations being transmitted through the terminal wires to the tubes, which might be damaged thereby, the wires are bent to form laterally projecting reverse bends that increase their resiliency, as shown in Figs. 9 and 12. The free ends of the tubes are cushioned by rubber pads 64 cemented thereto and engaging plate 58 and the front wall of the case.

The upper end of plate 58 is provided with a recess across the back of which a thinner insulating member 66 is fastened. This recess contains a knurled wheel 6'! that is rotatably mounted on member 66 with a grounded thin metal electric shielding plate 65 of approximately the shape of member 66 between them. By mounting the wheel in a recess in this manner the wheel does not project so far forward from the plate whereby an appreciable amount of space is saved. This is very important in helping to streamline the hearing aid design, and it makes the best possible utilization of the space available in the case. Wheel 51 carries a radially projecting lug 68 that has transient engagement with the bifurcated arm of a tiny bell crank 69 having a shaft pivotally mounted in the plate. The other arm of the crank is urged in opposite directions from a dead center position by means of a U-shape spring 10 connected thereto and to the plate. The crank is swung by lug 68 from its extreme positions to slightly past dead center, whereupon the spring snaps it the rest of the way. When the crank is moved, it swings a contact arm 12 (Fig. 8) connected to shaft 80 at the back of the plate to move its contact button 13 into and out of engagement with an electric contact 14 resiliently supported by a formed leaf spring 83 also mounted on the plate and thus forms the switch 48 (Fig. 4) for the filament circuit of the tubes. The contacts 13 and 14 are made of a suitable electric contact material such as fine silver, and have contact surfaces that are essentially spherical in shape. These contacts make wiping contact with each other and thereby keep their surfaces clean. This is particularly important at the low potentials and currents required by the hearing aid tube filaments. To provide a positive, unvarying connection to contact arm 12 from one side of the circuit, a spiral lead H encircling shaft 80 behind crank 69 is attached at its inner end to the crank and at its outer end to a suitable terminal on plate 58. The crank is spaced from the plate by a shoulder on shaft 80 to provide clearance for the spiral. This type of switch is especially adapted for useon a thin supporting plate, and has proved to have a life far in excessof any requirements that could be imagined for hearing aid use. As shown in Fig. 8, the shaft 84 of wheel 61 projecting through member 66 carries a control arm 15 that slidably engages a semi-circular resistance element 16 mounted on the back of member 66. Control arm 15 consists of a number of spring wires suitably formed to make smooth contact with the resistance element. These wires are riveted and soldered into a slot 85 in the side of shaft 84 (Fig. 8) Thus, when the control wheel is turned, it first closes switch 48 and then moves the sliding contact along the resistance element to serve as the volume control 31 (Fig. 4) of the hearing aid.

Mounted beside the control wheel on the front of plate 58 is a manually operable tone control lever T1 that projects through a slot 18 (Fig. in the side of the case. This lever is connected to a contact arm '89 at the back of the plate that forms the switch arm of the tone control switch 21 (Fig. 4).

All of the rest of the electrical elements of the amplifier circuit, such as the various condensers, resistors, sockets and their connecting wiring shown in Fig. 4, are mounted on the back of the plate 58 in the rear compartment where they are protected from humidity changes, perspiration, dust, and the like. Also, they are not exposed to tampering or accidental injury when the case is opened to change a tube. The seven electric sockets 39 are mounted in a row along the lower end of the plate in line with openings 82 in the end wall of the back section of the case for reception of the contact pins on the plugs by which the receivers and batteries are connected to the amplifying unit. In case a bias cell 8! is used, as is sometimes desirable, the plate may be provided with an opening for snugly receiving a portion of the cell so that it will not project too far from the back of the plate.

With a hearing aid constructed in accordance with my invention, the microphone, tubes, amplifier unit and rear case section may be individuall-y replaced by persons who are trained but who are not necessarily technically skilled. This requires them to keep only a few spare parts on hand and makes it unnecessary to return the instrument to the factory for repair. The readily interchangeable front section of the case with the microphone carried thereby makes it possible for a dealer in fitting a customer to try several different microphones having different response characteristics until he finds one best suited to the customers needs. By placing all of the wiring on one side of plate 58 with all of the components laid down fiat against it, any one component can be quickly and easily reached for servicing or replacement. Although this is generally done only at the factory, the entire amplifier unit is replaced in the field and returned to the factory, so the user has immediate use of his hearing aid again. The front of the plate is kept clean and clear of parts that might be damaged or interfered with when the front of the case is removed to permit tube replacements. The volume control, being sealed in the back of the case, is protected from dirt and dust that might interfere with its operation. The advantages of being able to use the same amplifier unit with either a magnetic or a crystal receiver are obvious.

According to the provisions of the patent statutes, I have explained the principle and construction of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a hearing aid, a case divided into front and back sections detachably connected together, a microphone therein attached to and supported only by said front section, an independently supported amplifier unit in the case detachably connected to said back section, and normally engaged separable members electrically connecting the microphone and amplifier unit, said members being adapted to be separated when the case is opened whereby to disconnect the microphone and amplifier unit.

2. In a hearing aid, a case divided into front and back sections detachably connected together, a microphone therein attached to said front section, an independently supported amplifier unit in the case detachably connected to said back section, a set of electric contacts connected to the microphone and mounted in said front section, and a set of electric contacts connected to the amplifier unit and carried thereby, said two sets of contacts engaging each other when the case is closed to electrically connect the microphone and amplifier unit, and said two sets of contacts separating when the case is opened whereby to automatically disconnect the microphone and amplifier unit.

3. In a hearing aid, a case divided into front and back sections detachably connected together, a microphone unit therein including a set of electric contacts and being attached to said front section, and an amplifier unit in the case including a set of electric contacts and being attached to said back section, said two sets of contacts being mounted in fixed position relative to the case and being located for engagement with each other when the case is closed to electrically connect the microphone and amplifier units, and said two sets of contacts separating when the case is opened whereby to automatically disconnect the microphone and amplifier units.

4. In a hearing aid, a case divided into front and back sections detachably connected together, a microphone unit therein including a set of electric contacts and being attached to said front section, and an amplifier unit in the case including a set of electric contacts and being attached to said back section, two of said contacts being metal pins and two of the contacts being metal sockets for frictionally receiving the pins when the case is closed to electrically connect the microphone and amplifier units.

5. In a hearing aid, a case divided into front and back sections detachably connected together,

a microphone therein attached to said front section, a plate in the case detachably connectd to said back section and spaced from the back wall of the case, amplifying elements mounted on the back of said plate, and separable means electrically connecting the microphone with the elements mounted on the plate.

6. In a hearing aid, a case divided into front and back sections detachably connected together, a microphone therein attached to said front section, a plate in the case detachably connected to the front of said back section and forming in the case a sealed rear compartment, amplifying elements mounted on the plate in said compartment, and means electrically connecting the microphone with the elements mounted on the plate.

7. In a. hearing aid, a case divided into front and back sections detachably connected together, a microphone therein attached to said front section, a plate in the case detachably connected to said back section and spaced from the back wall of the case, resistors and condensers and connecting Wiring mounted on the back of said plate within said back section, amplifier tubes detachably mounted on the front of the plate, and means electrically connecting the microphone with the elements mounted on said plate.

8. In a hearing aid, a case divided into front and back sections detachably connected together, a microphone unit therein including a set 01"" electric contacts and being attached to said front section, a plate in the case detachably connected to said back section and spaced from the back wall of the case, all of the resistors and condensors be ing mounted on the back of said plate within said back sec-tion, amplifier tubes detachably mounted on the front of the plate, and a set of electric contacts electrically connected to the elements mounted on said plate, said last mentioned contacts being mounted on said plate and frictionally engaging said first-mentioned set of contacts.

9. In a hearing aid, 9, case having a slot in its upper end and divided into front and back sections detachably connected together, a microphone in the upper part of the case attached to said front section, a plate in the case detachably connected to said back section and spaced from the back wall of the case, amplifying elements mounted on the back of said plate within said back section, amplifier tubes detachably mounted on the front of the plate below the microphone, said plate being provided with a recess in its upper end behind the microphone, a supporting member secured to the rear face of the plate and extending across said recess, a manually operable electric circuit controlling member disposed in said recess and rotatably mounted on said supporting member, said control member projecting through said slot, and means electrically connecting the microphone with the elements mounted on said plate.

10. In a hearing aid, a case having a. slot in its upper end and divided into front and back sections detachably connected together, a microphone in the upper part of the case attached to said front section, a plate in the case detachably connected to said back section and spaced from the back Wall of the case, amplifying elements mounted on the back of said plate within said back section, amplifier tubes detachably mounted on the front of the plate below the micro phone, said plate being provided with a recess in its upper end behind the microphone, a supporting member secured to the rear face of the plate and extending across said recess to close the back of it, a manually operable electric circuit controlling member disposed in said recess and rotatably mounted on said supporting member, a grounded electric shielding plate between said circuit controlling member and said supporting member, said control member projecting through said slot, a volume control unit mounted on the back of said supporting member and operated by said controlling member, and separable means electrically connecting the microphone with the elements mounted on said plate.

11. In a hearing aid, the combination with a microphone, an amplifier, and a supporting plate, of an electric switch and volume control unit mounted on said plate, said unit comprising a spring-mounted electric contact on the back of the plate, an oscillatable electric contact arm adapted to be swung into engagement with said contact, a shaft journaled in the plate and carrying said arm, an oscillatable member rigidly connected to the outer end of the shaft for swinging the arm, a spring for swinging said member in opposite directions from a dead center position, manually rotatable means having transient engagement with said member for swinging it against the resistance of said spring until it passes dead center, an electric control arm carried by said rotatable means behind the plate, and an electric resistance element slidably engaged by said control arm.

SAMUEL F. LYBARGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,688,976 Lum Oct. 23, 1928 2,122,429 Lieber July 5, 1938 2,251,928 Field Aug. 12, 1941 2,302,113 Faltico Nov. '7, 1942 2,319,627 Perlman May 18, 1943 2,321,370 Dubilier June 8, 1943 2,327,320 Shapiro Aug. 17, 1943 2,327,321 Shapiro Aug. 1'7, 1943 2,386,705 Merrill Oct. 9, 1945 

